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I purchased a 2018 Giant Quick e+ for commuting. Giant uses a modified yamaha PW-X system they have branded "syncdrive pro". The bike is great but the headlight it comes with stinks. I would like to drive a light with more lumens off the battery. The yamaha system uses a 36V battery that it drops down to 6V for the headlight (and presumably the tail-light).

For the 6V systems there are some options including lights from lupine SL S Yamaha E-Bike Light (500 lumen) and supernova mini2 (235 lumen). I am getting one of of lupine lights to see if 500 Lumen is enough.

The question: I am not sure why Yamaha decided to use 6V internally, except for perhaps cost. You can buy a 36V DC to 12V DC converter that is waterproof. IF installed the converter (and find a place for it) it seems reasonable that I could rewire the bike to use a 12V light. This would let me have a light that drives up to 1100 lumens. Am I completely nuts or is this reasonable?

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    Thinking you need 1100lumens for commuting is nuts. An H4 car headlight on low beam produces 1000 lumen. A US HB1 on high bean produces 1200lumen. Car headlamps are carefully engineered to throw the light so they avoid blinding oncoming drivers, unlike most bicycle lights.
    – mattnz
    Oct 27, 2018 at 2:01
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    You can fit any battery-powered light you want, without having to mess around with the bike's power system. Plus its an independent battery that won't die if the main one dies. Downside, two batteries to charge.
    – Criggie ♦
    Oct 27, 2018 at 7:51
  • Consider that you'll utterly void any warranty by messing with the wiring.
    – Criggie ♦
    Oct 27, 2018 at 7:51
  • Not a duplicate, but related. bicycles.stackexchange.com/questions/51016/…
    – Criggie ♦
    Oct 27, 2018 at 7:52
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    And 6 watts of 6 volt AC is the standard for a dynamo-equipped bike, where 1.5W goes to the rear light and 4.5 is used by the front light. So guessing you're in Europe where such lights are more common.
    – Criggie ♦
    Oct 27, 2018 at 7:53

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The answer to your question is that 12V is not the standard for bicycle lights. 6V is. There are a lot of very good 6V cycle lights designed for dynamo power (I don't know enough about the Yamaha/Giant wiring to know how they connect to lights). Or you can get a separate battery powered light (again, lots of very good options available).

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